1.A rectangular lawn is 14m long and 10m wide. A strip of uniform width is mowed around the outside of the lawn. How wide is the strip when the area of the unmowed portion of the lawn is 12m2次
2.The square of the largest of three consecutive integers is 140 less than the sum of the squares of the two smaller integers. Find the three integers.
maths
2010-09-04 5:57 am
回答 (3)
2010-09-04 3:21 pm
✔ 最佳答案
1.Let width of strip = x.
Width of unmowed area = (10 - 2x)
Length of unmowed area = (14 - 2x)
so (10 - 2x)(14 - 2x) = 12
(5 - x)(7 - x) = 3
35 - 12x + x^2 = 3
x^2 - 12x + 32 = 0
(x - 4)(x - 8) = 0
x = 4 or 8 (rej. since 2x > 10)
2.
Let the 3 consecutive integers be (x - 1), x, (x + 1)
(x + 1)^2 + 140 = x^2 + (x - 1)^2
x^2 + 2x + 1 + 140 = x^2 + x^2 - 2x + 1
x^2 - 4x - 140 = 0
(x + 10)(x - 14) = 0
x = - 10, or 14.
so the 3 integers are : 13, 14, 15 or - 11, - 10, - 9.
2010-09-05 1:39 am
2010-09-04 7:52 am
Hard to understand what's Q1 talking about...=="
收錄日期: 2021-04-22 00:50:18
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20100903000051KK01498